Plural stage refrigeration system and control therefor



PLURAL STAGE REFRIGERATION SYSTEM AND CONTROL THEREFOR Filed July 19, 1943 Nov. 2, 1-948. w. L. McGRATH 3 Sheets-Sheet 1 Nov, 2, 1948. V w. L. M GRATH 2,

PLURAL STAGE REFRIGERATION SYSTEM AND CONTROL THEREFOR Filed July 19, 1943 3 Sheets-Sheet 2 Ottomeg Nov. 2, 1948. w. L.MGRATH v PLURAL STAGE REFRIGERATION SYSTEH AND CONTROL THEREFOR Filed July 19, 1943 3 Sheets-Sheet 3 inventor WILLMM L. M9 (M1727! Patented Nov. 2, 1948 2.453.095 r1. STAGE narmoaan'rron SYSTEM AND con'raor. 'rnaanroa William L. McGrath, Philadelphia, Pa., assignor Minneapolis, Minn., a corporation of Delaware Application July v19, 1943, Serial No. 495,246

, 20 Claims. ((162-115) a l :2 Multiple stage refrigeration system have long operation until conditions are favorable. thereby been used to reach temperatures lower than can be eliminating the need for unduly large motors.

attained by a single stage, but there is a demand It is well known that the cooling abilities of the at present for systems that will not only refrigerrefrigerator evaporator depend on the quantity of ate to very low temperatures but which will also refrigerant pumped through same and upon the give controllable cooling over an extensive range pressure conditions under which it is'pumped. of temperature from the lowest obtainable by the Thus, it isan object of this invention to control equipment up to room temperatures. Refrig- .the capacity of arefrfgeration'system by control-- era'tion systems of this sort are particularly useful ling the pumping of refrigerant.

in chemical and metallurgical practice, for re- It is a further object to control the pumping oi search, and for testing instruments and other a fluid in a plural sta e pumpin system by Opel equipment used in aviation. Further, even in ating the pumping units in sequence and sequensuch common uses as cold storage, the refrigeratially controlling by passes around certain of the tion equipment is required to be flexible in capacp mping-units. r ity, due to the varying kinds and quantities of It is still another object to provide a system of material that may be handled, emcient as possible control for pluralstage refrigeration systems hav at any capacity and accurately controllable at any ing a plurality ofevaporators with individual canchosen control point. Optimum storage ,temperatrol for each evaporator.

tures for various products vary considerably and It is a further object of this invention to provide many products require an initial curing temperaa plural stage refrigeration system which may be ture, a storage temperature, and in some cases, a controlled by electric or pneumatic means, or by a finishing oil temperature. Highly accurate concombination of such means.

trol permits close adherence to optimum tempera- These and other objects will become apparent tures and often permits prolonging the storage upon a study of the drawings and specification of period for months. Obviously, these are merely the present invention.

examples to illustrate the utility of refrigeration Figure 1 is a schematic view of a three stage systems of the sort about to be described. plural evaporator refrigeration system'controlled It is therefore an object of'the present invention by pneumatic means. q l

to provide an improved and readily controlled Figure 2 is a view similar to Figure l but showplural stagerefrigeration system. ing a two stage system incorporating almodifled It is a further object to s-ocontrol a plural stage pneumatic system. and

refrigeration system that only the required Figure 3 shows a refrigeration system similar amount of refrigeration, at any chosen control ,to that of Figure 2 but using electric instead of point,'wi11 be furnished, thereby saving power and pneumatic control. facilitating the control of the equipment. .m Referring to Figure 1 it is noted. that three Another object of this invention is to control a compressing units are used to supp y vt v l plural stage refrigeration system by throttling orators, the evaporat rs bein i d vi l y n each stage of the system as it is placed into operat d by a t ol system comprisin pneu tion thereby giving regulation or the system from matic means. However. i Should b n ted that zero to one hundred per cent of its capacity. 40 the figure s illustrative only and that o 1 It is another object or thisinvention to provide mor ompr sso u s may b s d a d the mod a system of control comprising fluid means 'to opof ntrolling the flow of refrigerant thr ugh he erate a controlled device from one extreme posivaporato which ay number one or o e. s

tion to its opposite extreme and then back to said immaterial so long as the control i n e p o e first extreme in a gradual manner asa modulat- 45 Sequence and f the Sor o be d scribed. ing controller moves from one of its extreme posi In Figure 1 pr s rs l, 2. and 3. dri n y tions t m other extremeposition, motors 4, 5, and B, are connected in series, 'com-' It is also one of the present objects to provide pr sso I being the lowest pressu e unit in the an improved plural stage refrigeration system Series and compressor 3 the highest o p sso composed of standard equipment, thus permitting 5o 3 discharges through pipe 1 into condenser 8 economies in the purchase oi. the equipment and from which refri'gerantis delivered through pipes facilitating installation and servicing. Further. 9 and 9a to expansion valves l0 and Him and because of the excellentcontrol provided, the low-' associated 'evaporators H and Ila, respectively. er pressure units may be constructed and powered As the piping and the controls relating to evap for their normal operation as they are not put in 6 orator Ila are similar to and function in the 3 same manner as the like parts relating to evaporator II, the refrigerant and control circuits of evaporator II only will be discussed, it being un-- orator II and additional evaporators similar to II and lid and of still different capacities may be connected in the same manner as the evaporators shown. Obviously, as evaporators II and lid are individually controlled they may, at any particular time of operation of the system, be

operating under different conditions. This will be brought out and made'clear in the operation schedule which followsthis description. From evaporator II, refrigerant flows through pipes I2, I3, and 3i to compressor I, said compressor 1 discharging through pipe I4, intercooler I5, and pipe l6 to the suction of compressor 2. Compressor 2 discharges through pipe l1, intercooler I3, and pipe I9 to-the suction of compressor 3, said compressor 3 discharging as before mentioned. A by-pass 29 is provided between pipe I2 and pipe I6 and comprises pipe 2 I, check valve 22, pressure control 23 and modulating valve 24, said valve being normally closed andsaid check valve 22 permitting flow from pipe I2 to pipe I6 only. A by-pass 25 is provided between pipe I2 and pipe I9, said by-pass 25 comprising pipe 26,'

check valve 21 and modulating valve 28, said valve being'normally closed and said check valve permitting flow from pipe I2 to pipe I9 only. A normally closed modulating valve 29 is provided in suction line l2 between by-pass 20and pipe I3. A pressure control 39, to govern the action of modulating valve 29, is inserted in suction line I3 between valve 29 and compressor I,

Motors 4, 5, and 3 are controlled by pressure switches 32; 33, and 34, respectively, the pressure switches being controlled by a control system incorporating thermostatic or other such means '35, said means 35 being supplied with air under pressure by pipe 36. Thermostatic means 35 regulates the pressure in branch pipe 31 in accordance with the demand for refrigeration as determined by said device 35. Branch control pipe 31 connects to pressure switch 34 by tube 38, and modulating valve 28 is connected-to said branch by tube 39. Tube 40 connects said branch and 3 are idle. the air pressure in branches 31 and 31a, is zero and the pressure of'the air supply is 15# per square inch. Upon a demand for refrigeration, as determined by thermostat 35, the air pressure in, branch 31 is increased by the action of said thermostat 35. At a one pound pressure in-branch 31, pressure switch 34 is actuated and starts motor 6 by the circuit: wire 43, wire 5i, wire'32, switch 34, 6, wire 39, and wire 43, thus placing compressor 3 in operation. As before stated, valves, 24, and 23 are each normally closed but are opened in response to sufficient air pressure. Valve 23 is opened by pressures from one to five pounds, being fully open at five pounds'persquare inch pressure. At one-pound pressure in branch 31, valve 29 is still closed but is about to open, valves 24 and 29 remain closed and compressor 3 is running under conditions tending to produce a vacuum in by-pass pipe 23 and pipe I9. With an increase in air pressure to two pounds in branch 21, valve 28 is opened partially and compressor 3 operates under conditions of light loading due to its suction being throttled by said valve 23. With a pressure in thebranch of live pounds, valve 23 is open and refrigeration is provided to the full mally'closed and is under control of pressure controller 23, said valve 24 being set to start opening at six pounds per square inch pressure and being fully opened at ten pounds per square inch pressure. Home, with six pounds per square inch pressure in branch 31, compressors 2 and 3 are operating, valve 28 is wide open and valve 24 31 to pressure switch 33, and tube 4i connects said branch to pressure controller 23. Tube 42, under control of controller 23, extends from same and connects to modulating valve 24 by tube 43,

connects to pressure switch 32 by tubes '44 and 45, and connects to pressure controller 30 by tube 46. Pressure controller 30 is connected to, and in control of, modulating valve 29, through tube 41. As before stated, the recitation of the refrigerating units and the control system has been given for that relating to evaporator I I only, and it is understood that similar parts bearing similar numbers including a relate in the same'manner to evaporator lid, and that other evaporators may be connected to the system in the same man- 1 ner, and controlled in like fashion, as said evaporators II or Ila. Further details of the control and operation of the above described system will be brought out and made more clear in the following operation schedule.

Operation of Figure 1 Under stand-by conditions, compressors I, 2,

is ready to open, and the system's capacity is that due to theoperation of compressor 3 alone. Compressor 2 has, added no capacity to the system due to its closed suction line; As the pressure in branch 31 rises above six pounds per square inch, valve 24 is proportionately opened and compressor 2 assumes increased load. The load on compressor 2 increase until the pressure rises to ten pounds in branch 31 and valve 24 is fully opened, at which point said compressor is loaded, as is compressor 3, and the system's capacity is that obtainable from the two compressors running together. As the pumping capacity of compressor 2 is increased there is a tendency for refrigerant to pass through by-pass 25 and into suction line I2 but this is prevented by check valve 21 which, as before stated, permits flow from pipe to I9 only. Pressure controller 23 is set to permit opening of valve 24 only when conditions of pressure in pipes 2I and I3 are such as to permit safe operation'of compressor 2.

With. an increase. in branch pressure to eleven pounds per square inch, compressor I is started by pressure switch 32 as follows: wire 49, wireIiI, wire 62, switch 32, wire 63, wire 64, motor 4, wire 60, and wire 48. As before noted, pressure switch 32 is actuated by air pressure from branch 31 through tube 4i, pressure controller 23, tube 42, tube 44 and tube 45, hence the action of pressure switch 32 is under the control of pressure controller 23; therefore, compressor I cannot be started unless pressures existing in pipe I6 and 2 I are such as to permit safe operation of comwire 53, wire 54, motor pressor 2. As before noted, the suction of compressor i is controlled by mbdulating valve 29, which is normally closed, he ce compressor I also starts up under conditi us or negligible load.

As the pressure in branch iilrises to fifteen pounds per square inch, valve 29 is driven toward open position and compressor i, assumes added load until, at said maximum control pressure, all three of the compressors are operating at full load and the system's capacity is at a maximum. check valve 22 prevents reverse flowthrough bypass 2d. Pressure control prevents valve 28 from opening until pressure conditions in pipes it and ti are low enough to permit safe operation of said compressor i.

In this operation schedule it has been assumed that there was no demand on evaporator Ha, as determined by thermostat 3511, but it should be noted that the system may be started up and its capacity varied to meet the demand of evaporator Ma in the same manner as before described. Further, it will be noted that with a demand in more than one evaporator at the same time the refrigerating system comprising the compressors will operate to supply the maximum demand, the refrigerant flowing through evaporators having a lesser demand being throttled to meet the demand of said evaporator. Assume that the ,demand at evaporator H, as measured by thermostat 85, is such as to require the operation of all three compressors, and that an initial demand has become apparent at thermostat a, thereby raising the pressure in branch 3'50. to one pound per square inch pressure. At this pressure, switch 34a. is actuated, said switch 3% permitting starting or motor 6 by the connections: wire t9,

wire ti, wire ma, switch 34a, wire 53a, wire 54, motor 8, wire 50, and wire it. As before noted, however, the motor is already running so switch K Na merely provides another circuit by which the motor runs. Valve 28a, being similar'to valve 28,

is closed but is ready to begin opening at one pound pressure. Valves 29a and 24a are both closed hence refrigerant may enterevaporator iia through pipe 9a and expansion valve Illa, but cannot-be evacuated therefrom, therefore no continuous refrigeration can take Place therein.

With a further increase in pressure in branch 31a to two pounds per square inch, valve 28a is partially opened and refrigerant may flow through same to the suction of compressor 3, the flow of refrigerant thereby permitting refrigeration in evaporator ila. As the Pr s ure in branch 31a continues to rise due to added demand, as measured by thermostat 35a, valve 28a is opened to its full capacity and if required, valves 24a and 29a. are opened in the same sequence as valves 24 and 29, before described. Check valves 21a. and 22a. prevent reverse flow through their respective by-passes in the same manner as previously described. Should the demand at evaporator ll be satisfied while evaporator Ha is still unsatisfied, then the operation I of the system will be regulated to satisfy the demand at evaporator Ila in the same manner as wag'described in the operation of the system relating to evaporator ll. As before noted,the present example. is givenas an illustration only V and is not intended to limit the scope of the invention. Other contrfolmeans which permit the same sequence of operation as the above described pneumatic system may be substituted therefor.

In review, upon a demand for refrigeration at 6 an evaporator, a compressor is started, the su tion of said compressor being throttled, initially, to a no load position said suction being throttled toward open position as the load demand increases until the full capacity under. the conditions of said compressor is reached. Should this capacity be inadequateto meet the demands at said evaporator, another compressor is started, said compressor being throttled as in the first example, the capacity of said second compressor being increased in response to demand as before.

, ndditional compressors may be started or stopped in a similar manner as the demand for refrigeration varies. With a demand at more than one evaporator, the system will operate to satisfy the most extreme conditions, the refrigerant passing through any individual evaporator being throttled to meet the need of said evaporator thereby giving smooth, flexible, control of a multi-stage refrigeration system in response to the demand of any one, or more than one. evaporator from minimum to maximum capacity. Thepresent control system involves the runningof no more compressors than are needed, each compressor added to the series being run at no more than sufflcient capacity in such manner that the present system provides an eflicient as well as smooth control.

a Figure 2 Figure 2 relates to a modified plural stage re-.

frigeration system comprising compressor 65, driven by motor 66, and compressor G'i driven by motor 68, compressor 6? discharging through pipe 69 to condenser iii, from which extends pipe H connecting with expansion valve 72; and evaporator 13. The outlet of evaporator '13 connects by pipel i to the suction of compressor 65. Com ,pressor discharges through pipe 15, intercooler 16 and pipe i1 into the'suction of compressor 67. A by-pass 18 comprising pipe 19,

and pressure actuated, modulating valve 80, is connected between suction pipe I4 and pipe 11. The controls comprise thermostat 8| having a 15 pounds per square inch air supply through tube 83, and controlling the pressure in branch 84.

Thermostat 8! comprises a bulb 82 which contains a volatile fluid and is connected to expansi- .bie bellows 85. Bellows 85 bears against bellcrank 81, the pressure of the bellows being resisted by adjustable spring 86. Bell-crank 81 transmits pressure due to spring 86 or bellows 85 to flexible diaphragm 89 through lever member 88, said pressure tending to move said diaphragm downwardly. Diaphragm 89 is associated with space I21. and air pressure within said space tends to move said diaphragm upwardly. An arm- 90 is attached to said flexible diaphragm 89 and extends into said space I21. Arm member 90, in a balanced position of diaphragm 89, bears against valve means 9i which controls bleedl outlet 92, and also bears against valve means M, which controls air supply 83. Spring 93 assists in holding one end of arm member 90 downwardly and against valve 94 to hold same closed. Arm member 90 is so proportioned and arranged that in the'balanced position of diaphragm 89,

valve 9| is also held closed. Thermostat 8! controls-the air pressure in branch 84, said branch 84 being connected to air space I21 of said thermostat.

Pressure switches I03 and 98, for motors 66 and 68, respectively, are connected by tubes I02 and 95 to branch 84.

75 A reverse acting relay I01 is connected to branch 84 by tubes I08 and I09 and controls valve 80 through tube IIII. Relay I01 comprises a housing II2 having therein, spaced, flexible, diaphragms H3 and H4 connected by a. longitudinal valve chamber II9, said valve II8 being urged, closed by spring I20. Lever II1 operates valve I2I, urged closed byspring I22, said valve being in valve chamber I23, which opens to the atmosphere through opening I I I. The remaining space between the diaphragms, I24, connects to valve 80 through tube IIII. Member H is normally urged downwardly by adjustable spring means I25, the motion being'resisted by air pressure within space I24 and within space I26, which Is connected to branch 84 by tube I08. Spring I25 is, in the present example, adjusted to maintain member I15 in its mid position when the sum of the pressures in space I24 and space I26 equals 15 pounds per square inch. When the sum of said pressures is less than 15 pounds per square inch, member I I5 i. driven downwardly and opens valve II8, to bleed more air into space I24 to,

increase the pressure therein, and to increase the totalvpressure opposing spring I25. When the sum of the pressures within said spaces I24 and I26 exceeds 15 pounds per square inch, member I I5 is moved upwardly, thereby opening valve I2I and bleeding air out of the space I24 to decrease the total pressure opposing said spring I25. For a fuller explanation of reverse acting relay I01, reference is made to Figure 4 of Joesting Patent No. 2,286,282, issued June 16, 1942. The relation of these various parts will be brought out in the following operation schedule.

' Operation of Figure 2 With thermostat 8| in a satisfied position, the pressure is low in bulb 82, bellows 85 is retracted, and bell-crank 81 imposes no pressure on diaphragm 89. l lssumin'g that thermostat 8| has just reached its satisfied condition, and that air pressure exists within space I21 and connected parts of the control system; said air pressure is reduced to zero as follows: air pressure within space I21 moves diaphragm 89 upwardly, when unopposed, and tends to move member 90 off of valves 9| and 94. However, spring 93 opposes upward movement of arm 90'at one end and tends to hold valve 94 closedbut permits valve 9| to open and bleed air out of the space I21 to the atmosphere; This action continues until the pressure (gauge) in space- I21 is reduced to zero and diaphragm 89 asumes its normal position, in which both valves 9I and 94 are closed. With zero pressure in space I21and connected parts of the control system, pressure switches I03 and 98 are open, and no compressors are operating.

With a modest demand for refrigeration, as measured by an increase in pressure in bulb 82, bellows 85 exerts a pressure against bell-crank 81 which is transmitted to diaphragm 89' and arm 90 and forces the same downwardly. Because of the offset relation of 'valves 94 and 9] to the center of diaphragm 89, and as member 90, in normal position of diaphragm 89, bears against said valves 9I and 94, motion of said diaphragm 89 downwardly results in a tipping motion 'of member 90, said member 90 fulcruming about valve 9| and tending to raise on of valve 94. Valve 94 is spring urged upwardly and follows said member against the action of spring 93.

air to enter space I21 through supply until a pressure of two pounds per square inch has'been built up in space I21 and the connected control system, through branch 84. Pressure switch 98, connected to branch 94 by tube 95, is set to operate at two pounds per square inch; hence-it now closes and completes a circuit starting motor 68 as follows: wire 91, wire I00, pressure switch 98, wire IIII, motor 68, wire 99, and wire 95. Pressure switch I02 is set to close at 7% pounds per square inch, henc. at two pounds per square inch control pressure, said switch is open and motor 88 is not running. Pneumatically operated modulating valve" is normally closedand is adjusted to open in proportion to pressure between two pounds and seven and one-half pounds per square inch. Valve 80 is actuated by air supply through tube II8 from relay I01. The air pressure in space I24 being zero, and the pressure in space I 29, connected to branch 84, being two pounds per square inch, member H5 is driven downwardly by spring I25 because the pressure in spaces I24 and I28 totals-less than fifteen pounds per square inch. As member I I5 is driven downwardly, valve H8 is opened and permits air to now from branch 84 through tube I09, space II9, pastvalve H8 and into space I24. As the air bled into space I24 is at only two pounds per square inch pressure, the total pressure of spaces I24 and I26 remains less than fifteen pounds per square inch, and member I I5 remains in its downward position, thus putting branch 84 into direct communication with valve 80 by the circuits: branch 84, tube I09, space II9, space I24, tube IIO, valve 80. As valve 80 only starts to open at two pounds per square inch pressure, it is still closed, and compressor 61, driven by motor 68; is running under conditions of no load due to closed suction means.

With an increase in pressure in branch 84, due to a demand by thermostat 8I, valve 80 will be proportionately opened, compressor 81 will be inch in the same manner as previously described.

Spring I25 is now resistedby a pressure of six pounds per square inch in space I28 and six pounds per square inch in I24 but as the sum of these pressures is still less than fifteen pounds per square inch. spring I25 still dominates the position of member I I5 and keeps same in a downward position. Communication still exists between branch 84 and tube I09, space II9, space I 24, tube III] and valve 80. At six pounds per square inch, valve 80 is more widely open, and compressor 81 is operating under conditions of heavier loading. v

When the pressure in branch 84 rises to seven and one-half pounds per square inch, due to increased demands for refrigeration, as measured by 8|, the air pressure in space I28 and space I24 rises to the same value. At this point. however, the sum of the pressure in spaces I26 and I24 equals fifteen pounds per square inch and balancesthe force due to spring I25. Member 5 therefore moves to an intermediate position and both valve -I I8 and I2I are closed. Valve 80, due

pressor 65 into operation. This compressor adds little, it any, capacity to the system because the pressure in 11 cannot rise due toopen valve 00.

With an increase in branch pressure to 8 pounds per square inch, due to further demandsior refrigeration, as measured by thermostat the pressure in space I26 rises to 8 pounds per square inch. As the sum of the pressures in spaces I24 and I26 'now exceeds fifteen, member H is driven upwardly and opens valve I2l,

thereby bleeding air out of space I24 to the at mosphere. This action continues until the pressure in space I24 is reduced to a value,=which, added to the 8 pounds per square inch of space I26, equals said fifteen. In this case, the pressure in 'I24will be reduced to 1 pounds per square inch before member H5 is again moved back to its mid position and both valves II8 and I2I are closed. with the reduction in pressure in space I24, valve 80 is partially closed, therebyrestricting return flow through by-pass 18. As return flow through by-pass 18 is restricted, compressor 65 assumes load and the system capacity is thereby increased.

With a further rise in branch pressure to ten pounds per square inch, the total pressure in spaces I26 and I24 again overcomes the spring.

I25, and H5 is moved upwardly. The upward] movement of member II 5 opens valve HI and bleeds air out of space I24 until thepressure therein, added to the pressure in space I26, equals fifteen, at'which point the pressures are balanced by spring I25 and member 5 is'again moved to its mid position. With ten pounds per square inch pressure in space I26, the pressure in space I24 becomes five pounds per square inch, and valve 80 is proportionately closed. Compressor 65 now'carries a greater share of the load, due to less gas passing through by-pass 18, and compressor 61 carries added load due to the increased pressure in suction 11, hence the system capacity is increased.

I When the pressure in branch 84, due to action of thermostat 8i, rises to fifteen pounds per but these have been ignored to simplify the description.

It will. be further noted that this arrangement" provldesa pneumatic control system of general utility in which a power means or motor means (valve 80) is caused to gradually move from a first position to a second position and back again upon a change in the main air pressure from zero to fifteen pounds per square inch.

. In the following Figure 3,'it will be shown how this same sequence of operation may be obtained by electrical means.

Fioure 3 Figure 3 shows the same refrigeration system as Figure 2 but with an electrical instead of a pneumatic control system. Refrigerating units J to I45 correspond to, and are connected in f the same manner as, respectively, units 65 to 80 in Figure 2. Of these units, only valve I45 is different from its counterpart, valve I45 being an electricallyoperated modulating valve whereas valve 80 is a pneumatically operated modulating valve. Electrical controlling means-for Figure 3 comprises a modulating controller I41 including temperature responsive means I48 and I48, movable arm I5I,and potentiometer coil I50, said a controller regulating a modulating step controller I52, having motor I53, said motor [being similar to that described in Patent No. 2,023,110, issued January 14, 1936, to D. G. Taylor. Step controller I52 has two switches, I64 and I55, op-

erated by cams I58 and I51, respectively, and also includes a pair of potentiometers I58 and I58.

Potentiometer I58 has a coil I60, arm I6I, and

terminals I62 and I63. Potentiometer I56 has.

coil I64,arm I65, and terminals I66 and I61. A double-throw two wire relay I68 is provided hav 'ing acoil I68 and switch terminals I10, "I, I12,

I13, I16, 'I11, and switch blades I14 and I15. Valve I is controlled by a modulating electric motor of the same type as I53. Valve I45 is normally closed and switch arms I14 and I15 of relay square inch pressure, the pressure in space I24 is bled to zero to offset the increase in pressure in space I26. At zero pressure, valve 80 is closed, and compressors and 61 are operating in series and delivering full capacity.

Reviewing the operation 'of Figure 2, note that an initial demand starts a compressor under conditions oi no load and then throttles the suction to permit the compressor to meet the demands,

if possible. If the demand be excessive for one compressor, another is started, but operates initially with no capacity because of an open bypass. As the demand rises, this by-pass'is throt- -iled towards closed position until the net capacity I of the two machines satisfies the load requirements. Obviously, additional compressors may be provided in this system, being connected in the manner suggested. The specific pressures mentioned in the above description are considered illustrative .only and any suitable pressures may be used. It is well known that control means of the sort described have'operating differentials I68 are normally biased to the right by spring I18.

Operation of Figure 3 Under stand-by conditions, controller I41 is in its satisfied position, expansiblebellows I419 are retracted, arm I5I is at the extreme right of coil I50, step controller I52 is at its extreme counterclockwise rotative position and switches I54 and I55 are open. Upon a, rise in temperature, bellows .3I4'6,expands, moving arm I5I to the left; and step controller l52, to match the movement of I5I, moves clockwise. A predetermined initial clockwise movement of cam I51 closes switch I55 which starts motor I33 as follows: wire I18, wire I62, switch I55, wire I83, motor I33, wire I8I, and wire I60. i I

The initial movement of the step controller also moves arms IN and I65, of potentiometers I56 and I 59, respectively, in a clockwise direction. Because of the biased position of relay I68, only potentiometer I58 is active. Potentiometer coil I64 has the same resistance as the coil in the modulating motor of valve I45 but has its resistance all arranged to be swept by the first half of the full travel of arm I65 so that half the full clockwise motion of step controller I52 will modulate valve I45 from closed to fully open position. The circuit controlling the modulating valve I45 comprises: arm I65, wire I84,.wire I85, valve I45, wire I86,terminal I16, arm I14, ter

minal I1I, wire I81, terminal I66, coil I64, terminal I61, wire I88, terminal I13, arm I15, terminal I11, wire I89, and valve I 45. .Thus it will be seen that as the temperature rises at I48, and arm I moves toward its mid-position, compressor I33 is placed in operation and its operation is regulated by valve I45'which is opened in response to increased demand up to a wide open position when armv .I5I is at the mid-point of its travel.

Upon the step controller being driven through more than half its clockwise moton, to keep step -with increased demand of controller I41, cam

necting the outlet of the evaporator to the suction means of the first compressor; by-pass same resistance as the coil in modulating valve I45 but having all its resistance in the latter half of the travel of arm IGI. for valve I45 with potentiometer I58 in command is: arm I6I, wire.l90, wire I85, valve I45, wire I86, terminal I16, switch arm I14, terminal I10, wire I9I, terminal I63; coil I60, terminal I62, wire I92, terminal I12, arm I15, terminal I11, wire I89, and valve I45.

Note that coil I60 is connected reverse to I64 so that relative to terminals I16 and I11, clockwise movement of arm I6I results in decreased resistance on the control side of the terminal I16 whereas if coil I64 were used, the same direction of motoin of arm I65 would result in an increase of resistance on the side of terminal I16. It will thus be seen that as the step controller advances through the latter half of its clockwise travel, valve I45 is modulated towards closed po sition. As stated in the operation of Figure 2, full capacity is reached when both compressors I and I32 are in operation and valve I45 is closed.

As in the system of Figure 2, additional stages may be provided by connecting the compressors in series, as shown, providing a by.-pass for each pair of compressors and providing modulating valve control of each by-pass, the travel interval of the step controller being divided by the number of stages used and suitable switches and relays provided for said additional stages, as herein suggested.

Note that here, as in the previous example, the output of a plural stage refrigeration system may be varied from zero to one hundred per cent of its capactiy in an efiective and practical manner and that the system comprises standard and readily available units for bothrefrigeration and con-.

The controlling circuit means Including a throttling valve connected between the main suction means and the means connecting the discharge means of the first compressor and the suction of the second compressor; control means for starting the second compressor, upon an initial demand for refrigeration, and for opening said throttling valve increasingly as the demand upon the second compressor increases, said contrpl means starting said first compressor when the load demand exceedsthe capacity of the second compressor, and means restricting return flow through said by-pass means toward said main suction means. V

, 2. In a refrigeration system, first and second compressors, means connecting the discharge means of the first compressor with the suction means of the second/conduit means connecting the discharge'means of the second compressor to a condenser, expansion valve and an evaporator, main suction means connecting the outlet of the evaporator to the suction means of the first compressor; by-pass means including a throttling valve connected between the main suction means andthe means connecting the discharge means of the first compressor and the suction of the second compressor; control means for starting the second compressor, upon an initial demand for refrigeration, and for opening said throttling .valve increasingly as the demand upon the second compressor increases, said control means starting said first compressor when the load demand exceeds the capacity of the second com- I pressor, and check valve means restricting return flow through said by-pass means toward saidmain suction means.

3. .In a refrigeration system, first and second compressors, means connecting the discharge means of the first compressor with the suction means of the second, conduit means connecting the discharge means of the second compressor to a condenser, expansion valve and an evaporator, main suction means connecting the outlet means of the evaporator to the suction means of the first compressor; by-pass means including a throttling valve connected between the main suction means and the means connecting the discharge means of the first compressor and the suction of the second compressor; control means for starting the second compressor, upon an initial demand for refrigeration, and for opening said valve increasingly as the demand upon the trol. Further, as noted in the above examples, the I claims.

I claim as my invention:

1. In a refrigeration system, first and second compressors, means connecting the discharge means of the first compressor with the suction means of the second, conduit means connecting the discharge means ofthe second compressor to a condenser, expansion valve and an evaporator, main suction means consecond compressor increases, said control means starting said first compressor when the load demand exceeds the capacity of the second compressor, said valve being increasingly closed as the load demand on the second compressor increases. 4. In a refrigeration system, a plurality of compressors, conduit means connecting said compressors in series, with the outlet means of one bein connected to the inlet means of another, a condenser connectedto the outlet means of the high pressure compressor in the series, a plurality of evaporators connected to said condenser, conduit means connecting each evaporator to the inlet means of the lowest pressure compressor in the series, by-pass' means connecting the suction means of each evaporator with the means connecting a pair ofcompressors, a throttling valve and a check valve in each by-pass, said check valves permitting flow only in a direction towards said compressors, and'control means responsive to a condition afiecte'd by said evaporators connected to sequentially control the by-pass valves associated with the is V evaporator-s and to sequentially'control said compressors.

' 5. Ina refrigeration system, means connecting a plurality of compressors in series including conduit means connecting-the outlet means of one compressor to'the inlet means oi the next higher pressure compressor, the highest pressure compressor of" the series discharging through a condenser, said condenser supplying liquid refrigerant to a-plurality of evaporato'rs, suction means connecting each oi. said evaporators to the inlet means or the low pressure compressor of the se-' niesgand individual by-pass means connectedto the suction means of each evaporator and the conduit means connecting. each pair of compressors, each by-pass means being-valve controlled.

6. In a refrigeration system. conduit means connecting a plurality oi. compressors in series, the highest pressure compressor of the series discharging through a condenser, said condenser supplying liquid refrigerant toa plurality of evaporators, suction means connecting each of said evaporators to the inlet means oi the lowest pres sure compressor in the series; separate by-pass means connected at one end to the means connecting each pair of compressors and connected at the other end to the suction means of'an evaporator, each by-pass means being valve controlled; and control means comprising meansre sponsive to a condition ailected by operation of said evaporators and connected for controlling the operation of the compressors in sequence, the highest pressure compressorbeing started first. .said control means also operating said by-pass valves in sequence, the valve associated with the' inlet of the highest pressure compressor being opened first.

"I. In a fluid pumping system, conduit means connecting a plurality of individually driven pumping units in series, the discharge of one unit being connected to the intake of the next adjacent unit, the intake of the low pressure end or the series comprising main suction means and the a discharge of the high pressure end of the series comprising main discharge means; intervening suction means connected with the means connecting each pair of pumping units, each of said intervening suction means being valve controlled; control means responsive to load demands causing operation of said pumping units in sequence starting with the discharge end of said series, said control means also operating said valves in similar sequence, said valve control means restricting pressors; valve controlmeans for each by-pass,-

and control means for operating said valve means in sequence in response to a load demand, each of meansi'or each by-pass: control means respon- -sive to load demands ioryoperating said valve means and for starting said compressors in sequence, the higher pressure compressor being started first and the valve in the by-pass associ-. ated with the suction of said higher pressure compressor being opened first, and flow control means rendering inoperative each by-pass as the compressor whose discharge means isassoclated with said by-pass reaches'iullcapacity.

10. Compressing meanscomprising first, second, and third compressors, each being individually driven, the .discharge means 0! the first connecting with the suction means of the second, the discharge means of the second connecting with the suction means of the third, and the third compressor discharging into main discharge means, the suction means of the first compressor comprising main suction means, first by-pass means including a throttling valve connecting said main suction means and the discharge means of the first compressor, second by-- pass means including a throttling valve connecting said main suction means and the discharge means of said secondcompressor; and control means responsive to rei'rigeration demands by which, upon an initial and increasing demand, said third compressor is started and the valve of said second'by-pass means is proportionately opened, upon a demand in excess of the capacity of said third compressor'said second compressor 'is started and the valve of said first by-pass means is proportionately opened, and upon demands in excess of the capacity of said two compressors said'flrst compressor is started. a

11. In a refrigeration system, conduit .means connecting twoindividually driven compressors in series; valve controlled Joy-pass means connecting the suction means and discharge: means of one 0! the compressors; control means come prising a modulating controller, a modulating device operated by' and in step with said con-,

trolling modulating means governing said valve,

said valve being proportionately openedas the load is increased onthe first compressor started, and relay means, controlled by said device for reversing the action 01 said valve upon said predetermined movement of said device. the valve being proportionately closed as said predetermined movement is exceeded.

12. In a system for compressing a fluid, conduit means connecting two compressors in series, a

. by-passconnection which diverts the flow of fluid said valve means restricting a return flow through its by-pass as each additional valve is opened.

9. In a system for compressing a fluid, conduit means connecting a plurality of individually driven compressors in series, one end of said series comprising main discharge means and the other end of the series comprising main suction means a by-pass associated 'with each pair'oi,

, connected compressors, each by-pass lay-passing all lower pressure compressors; valve control around the lower pressure compressor and directs it to the intake of the higher pressure compressor, valve means in said by-pass connecton, controlmeans progressively opening said valve means in response to an increase in demand when the high pressure compressor only is operating, and con- 15 when the other pumping unit is operating, and to start the one pumping unit when said valve means is wide open, said control means progressively closing said valve means in response to an increase in demand when both said pumping units are operating.

ing unit is increased.

15. A fluid compressing means comprising twoindividually driven compressors connected in series; valve controlled by-pass means connected to the suction means and discharge means of one of the compressors; a control means supplying air under pressure in accordance with load conditions, a first pressure switch constructed and "arranged to start a first compressor upon an initial increment of air pressure, a' second pressure switch constructed and arranged to start the second compressor at a predetermined air pressure, said valve being opened in proportion to the air pressure increase until a pressure is reached near said predetermined pressure, and relay means reversing the effect of further increased air pressure and causing said valve to close in proportion to said further increased air pressure.

16.'In a refrigeration system, conduit means connecting first, second and third compressors in series, conduit means connecting the third compressor to a condenser, expansion valve and an evaporator, main suction means connecting the outlet of the evaporator to the suction means of the first compressor; first intervening conduit means connecting saidmain suction means and the means connecting the first and second compressors, second intervening conduit means connecting said main suction means and-the means connecting the second and third compressors, each of said intervening conduit means including a throttling valve; and control means comprising means for starting said third compressor upon an initial demand for refrigeration, said control means also controlling the throttling valve in said second intervening conduit means, said valve being increasingly opened in accordance with added demand on said third compressor; said control means starting the second compressor upon a demand in excess of the capacity of the third compressor, said control means throttling the valve in first intervening conduit means, and means restricting reverse flow through the second intervening conduit means toward said main suction means; said-control means, upon a demand for refrigeration in excess of the capacity of said second and third compressors, starting said first compressor, and valve means restricting return fiow through said first intervening conduit meanstoward said main suction means.

17. In a fluid pumping system, conduit means connecting first, second, and third individually driven compressors in series, the discharge means of the first compressor being connected to the suction'means of the second, the discharge means of the second being connected to the suction means ofthe third, the discharge means of the third compressor comprising main discharge means, and main suction means associated with the suction means of the first compressor; first intervening conduit means comprising a normaily closed throttling valve and a check valve. said conduit means being connected to the main suction means and'to the means connecting the discharge means of the first compressor and the suction means of the second compressor, second intervening means including a normally closed throttling valve and a check valve connected between said main suction means and the means connecting the discharge means of the second compressor and :the suction means of the third compressor, and normally closed throttling valve means in the suction means of the first compressor; control means comprising a supply oi air under uniform pressure, a controller responsive to'load conditions regulating the pressure of air in a control branch in response to the said conditions, a pressure switch operative at a low branch pressure to start the third compressor, a second pressure switch operative at a higher branch pressure to start said second compressor and a third pressure switch operative at a still higher branch pressure to start said first compressor, the valve in said second intervening con- "duit means being adjusted to be gradually opened with increase of branch pressure and to reach full open position at the pressure required to start the second compressor, the valve in the first intervening conduit means being adjusted to start opening at the pressure required to start the the controlbranch, and limit control means preventing operation of the first and second" compressors in the event of high suction pressures for same.

18. In a refrigerating system, conduit means connecting a plurality of individually driven compressors in series, the discharge means of one compressor being connected to the intake means of the next adjacent compressor, the intake means of the low pressure end of the series comprising main suction means and the discharge means of the high pressure end of the series comprising main discharge means; intervening suction means connected with the means connecting each pair'of compressors and the main suction means, each of said intervening suction means being valve controlled; control means responsive v todemands for refrigeration causing operation of said compressors in sequence starting with the discharge end of said series, said control means also operating said valves in similar sequence, said valve control means restricting return flow through each of said intervening means toward the main suction means as additional valves are opened.

19. In a fluid pumping system, conduit means connecting two individually driven compressors in series; valve controlled by-pass means connecting the suction means and discharge means of one of the compressors; control means comprising a modulating controller, a modulating device operated by andin step with said controller, the initial movement of said device from one extreme position, upon operation by said controller, operating means to start acompressor, a predetermined movement of said device starting the second" compressor, said device also controlling 17 modulating means governing said valve, said valve being proportionately opened as the load is increased on the first compressor started, and switching means controlled by said device for reversing the action of said valve upon said predetermined movement of said device, the valve being proportionately closed as said predetermined movement is exceeded.

20. In a refrigerating system, conduit means connecting first, second, and third individually driven compressors in series, the discharge means of the first compressor being connected to the suctionmeans of the second, the discharge means of the second being connected to the suction means of the third, the discharge means of the third compressor comprising main discharge means, and main suction means connected to the suction means of the first compressor; first intervening conduit means comprising a normally closed throttling valve and a check valve in series therewith, said conduit means being connected to the main suction means and to the means connecting the discharge means of the first compressor and the suction means of the second compressor, second intervening means including a normally closed throttling valve and a check valve in series connected between said main suction means and the means connecting the discharge means of the second compressor and the suction means of the third compressor, and normally closed throttling valve means in the suction means of the first compressor; control means comprising a supply of air under uniform pressure, a controller responsive to refrigeration demand for regulating the pressure of air in a control branch in response to said refrigerating de-- mand, a pressure switch operative at a low pressure in said branchto start the third compressor,

pressure to start said second compressor and a third pressure switch operative at a still higher pressure to start said first compressor, the valve in said second intervening conduit means being adjusted to be gradually opened with increase of branch pressure and to reach full open position at the pressure required to start the second comcompressor and to reach full open position at a second pressure switch operative at a higher pressor, the valve in the first intervening conduit means being adjusted to start opening at the branch pressure required to start the second the pressure required to start the first com pressor, the valve in the suction means of the: first compressor being adjusted to start opening at the pressure required to start the first compressor and to be fully open at the maximum pressure in the control branch, and control means preventing operation of the first and second compressors in the event of high suction pressures for the same.

WILLIAM L. McGRATH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent N 0. 2,453,095. November 2, 1948.

WILLIAM L. MCGRATH It is hereby certified that errors appear in the above numbered patent requiring a correction as follows:

i t In the drawings, Sheet 2, Fig. 2 should appear as shown below instead of as in the patent a; column 4, line 60, after the words from pipe insert the numeral 12;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of March, A. D. 1949.

THOMAS EMURPHn Aau'stantflommz'ssz'onenofPateMa; r 

